The effect of trace Co and Ni on the anaerobic digestion of straw.

The effects of trace metals on the process of anaerobic digestion for straw were studied under the conditions of adding Co,Ni and the mixture of Co and Ni.The COD_(Cr),the pH,the volatile fatty acid(VFA) and the biogas yield were analyzed under the anaerobic digestion condition.The results showed that the biogas yield rate increased by 39.0%,74.5% and 115.0% respectively as Co or Ni or Co+Ni was added in digestion system.Percentage of methane gas increased respectively to 50%,52.2% and 62.5% from 44.9%,VS removal ratio improved respectively to 46.2%,47.6% and 53.2% from 39.3%,and COD_(Cr) reduction ratio increased respectively to 56.9%,57.0% and 58.9% from 42.4%.It indicated that the process of anaerobic digestion for straw was improved remarkably by adding trace Co and Ni.The three different adding ways had different effects on the system.According to the comprehensive analysis of experimental results,adding the mixed trace metals of Co and Ni is an effective approach to improve the anaerobic digestion of straw and biogass yield rate.